I agree with Boan as well.
Because our spirits are eternal, there wouldn't be the need for age because we would live onto infinity. And, when we die and go to Heaven there is no such thing as time, because God doesn't have an age, He's infinite.
And he lives outside of time, He's not hindered by it.
Also, if we did have an age for eternity...imagine how big those numbers would be.
Example:
Age: 1,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000+
Lol...I don't even think there is a number for that ^!